Cartesian loop gain control devices are used in particular in mobile equipment of radiocommunication systems in which the gain control needs to be precise and have a wide dynamic range.
For example, a “Zero-IF” type radio transmitter in which baseband signals are directly transposed to the transmission frequency without passing through any intermediate frequencies, the gain control is divided over a number of voltage boosting analogue stages, or variable gain amplification (VGA) stages, to total 75 dB of functional dynamic range in 1 dB steps within the framework of the WCDMA (Wideband Code Division Multiple Access) standard. Such an architecture involves high current consumption and requires a large area of silicon.
Moreover, the increase in bit rates in telecommunications is accompanied by non-constant envelope modulations which require linear processing. Consequently, use is made of linearization devices such as, in particular, Cartesian loop devices which are normally implemented in the form of analogue circuits. This requires a footprint and a level of consumption that are incompatible with the current integration trends in mobile equipment.
Recently, Cartesian loop linearization devices which use digital components have been described, e.g., in U.S. Patent Publication No. 2004/0166813 A1.
Such known devices include a digital processing circuit which is suitable for receiving baseband input signals and Cartesian feedback signals, and which includes a stage for combining the baseband input signals and feedback signals to generate error signals. This digital processing circuit is linked via an analogue/digital and digital/analogue conversion stage to an analogue processing circuit. This analogue processing circuit is suitable for receiving the error signals and includes an output stage for generating an output signal from the error signals, and a feedback stage for generating the feedback signals from the output signal.
Such a device can be used with a conventional gain control including a number of analogue amplification stages, which raises the problems of consumption and footprint mentioned above. In particular, these consumption and footprint problems run counter to the trends towards increased integration in terms of footprint for reducing fabrication costs with a view to use in a mobile device such as a mobile telephone, for example.